Air gap semiconductor structure and method of manufacture

ABSTRACT

An air gap semiconductor structure and corresponding method of manufacture. The method includes forming a sacrificial polymer film over a substrate having metal lines thereon. A portion of the sacrificial polymer film is subsequently removed to form first spacers. A micro-porous structure layer is formed over the substrate and the metal lines and between the first spacers. A portion of the micro-porous structure layer is removed to form second spacers. The first spacers are removed by thermal dissociation to form air gaps. A dielectric layer is formed over the substrate and the metal lines and between the second spacers.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 90100427, filed Jan. 9, 2001.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a metal-oxide-semiconductor structure and corresponding method of manufacture. More particularly, the present invention relates to an air gap semiconductor structure and corresponding method of manufacture.

2. Description of Related Art

Following the rapid reduction of semiconductor line width, the accompanied increase in resistor-capacitor (RC) time delay has greatly reduced the operating speed of integrated circuits. To reduce RC time delay, methods that can lower resistance is frequently adopted. The most common trend now is to replace conventional aluminum wires by copper wires.

A second way of reducing RC time delay is to reduce capacitance between conductive wires in a multi-layer design. Conventional silicon dioxide is no longer versatile enough for this purpose because silicon dioxide has a relatively high dielectric constant. In general, low dielectric constant organic or inorganic material is used to form inter-metal dielectric layer. However, a medium having the lowest dielectric constant is air (a dielectric constant of 1). Therefore, air is ideal dielectric medium for lowering the capacitance of a capacitor.

Although air is the best dielectric material for lowering capacitance, overall mechanical strength of the device is reduced correspondingly. A weakened structure can have serious effect in various aspects of subsequent integrated circuit fabrication.

A device having air as a dielectric medium generally has air gaps between metallic lines. Air gaps will destabilize the semiconductor device and lead to structural deformation. Moreover, the air gaps are normally distributed all over the substrate. Although capacitor has low capacitance when air is used as a dielectric medium layer, poor heat conductivity of air often leads to a rapid accumulation of heat and a rise in temperature during operation.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide an air gap semiconductor structure and corresponding method of manufacture. The method includes forming a sacrificial polymer film over a substrate having metal lines thereon. A portion of the sacrificial polymer film is subsequently removed to form first spacers. A micro-porous structure is formed over the substrate and the metal lines and between the first spacers. A portion of the micro-porous structure layer is removed to form second spacers. The first spacers are removed by thermal dissociation to form air gaps. Finally, a dielectric layer is formed over the substrate and the metal lines and between the second spacers.

In this invention, air gaps are only formed on the sidewalls of the metal lines. Other sections of the substrate are covered by conventional dielectric material. With this arrangement, not only can RC delay be lowered to increase operating speed of integrated circuits, mechanical strength of the integrated circuit can also be maintained.

In addition, the micro-porous structure layer increases the diffusion efficiency of by-products generated during the dissociation of the sacrificial polymer film, especially in the region between neighboring metal lines where height/separation ratio is high.

Furthermore, since only spacer-like air gaps are formed on the sidewalls of the metal lines, heat generated during device operation can easily be channeled away through surrounding conductive layer. Hence, heat dissipation problem can be ignored.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,

FIGS. 1 through 6 are schematic cross-sectional views showing the progression of steps for manufacturing an air gap semiconductor device according to one preferred embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

FIGS. 1 through 6 are schematic cross-sectional views showing the progression of steps for manufacturing an air gap semiconductor device according to one preferred embodiment of this invention.

As shown in FIG. 1, a substrate 100 having metal lines 102 thereon is provided. The substrate 100 can be a semiconductor layer having multi-layered interconnects, for example. A sacrificial polymer film 104 is formed over the metal lines and the substrate 100. The sacrificial polymer film 104 is a low temperature dissociation polymer layer formed, for example, by spin-coating. The sacrificial film 104 can be a material layer having a dissociation temperature between 300° C. to 430° C., for example, polynorbornene.

As shown in FIG. 2, a portion of the sacrificial film 104 is etched back to form first spacers 104 a on the sidewalls of the metal lines 102.

As shown in FIG. 3, a micro-porous structure layer 106 is formed over the substrate 100 and the metal lines 102 and between the spacers 104 a. The micro-porous structure layer 106 can be formed, for example, by spin-coating. Materials that may form the micro-porous structure layer 106 include inorganic porous silicon dioxide and organic porous material, for example, Sol-gel, Xerogel, porous polyimide and porous methyl silsesquioxane (MSQ).

As shown in FIG. 4, a portion of the micro-porous structure layer 106 is removed by etching back to form second spacers 106 a on the sidewalls of the first spacers 104 a.

As shown in FIG. 5, the substrate 100 is put inside a furnace and heated to between about 400° C. to 450° C. The sacrificial spacers 104 a dissociate into small molecular weight by-products (not shown). By diffusion, the by-products penetrate through the second spacers 106 a into outer regions. Ultimately, the space originally occupied by the first spacers 104 a is turned into air gaps 108.

As shown in FIG. 6, a dielectric layer 110 is formed over the substrate 100 and the metal lines 102 and between the second spacers 106 a. The dielectric layer 110 can be a silicon dioxide layer formed, for example, by plasma-enhanced chemical vapor deposition (PECVD) or spin-on-glass (SOG).

By forming porous second spacers 106 a over the first spacers 104 a before the dielectric layer 110, by-products of dissociation can easily vacate from the space originally occupied by the first spacers 104 a. This is particularly important for diffusing by-products away from a region having a high aspect ratio such as the space between neighboring metal lines.

In summary, the advantages of the invention includes:

1. Air gaps are only formed on the sidewalls of the metal lines. Other sections of the substrate are covered by the conventional dielectric material. With this arrangement, not only can RC delay be lowered to increase operating speed of integrated circuits, mechanical strength of the integrated circuit can also be maintained.

2. The micro-porous structure layer increases the diffusion efficiency of by-products generated during the dissociation of the sacrificial polymer film, especially in the region between neighboring metal lines where height/separation ratio is high.

3. Since only spacer-like air gaps are formed on the sidewalls of the metal lines, heat generated during device operation can easily be channeled away through surrounding conductive layer the air gaps. Hence, heat dissipation problem can be ignored.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

What is claimed is:
 1. An air gap semiconductor device, comprising: a substrate having a plurality of metal lines thereon; a micro-porous structure layer between each two of the metal lines, wherein a first end of the micro-porous structure contacts with top corners of the metal lines, and a second end of the micro-porous structure contacts with the substrate, with a plurality of spacer-like air gaps located between the micro-porous structure and the metal lines; and a dielectric layer over the substrate covering the metal lines and the micro-porous structure layer.
 2. The device of claim 1, wherein material constituting the micro-porous structure layer includes porous inorganic silicon dioxide.
 3. The device of claim 1, wherein material constituting the micro-porous structure layer includes porous organic compound.
 4. The device of claim 3, wherein the porous organic compound includes polyimide.
 5. The device of claim 1, wherein the dielectric layer includes a silicon dioxide layer formed by plasma-enhanced chemical vapor deposition.
 6. The device of claim 1, wherein the dielectric layer includes a silicon dioxide layer formed by spin-on-glass method.
 7. The device of claim 3, wherein the porous organic compound includes porous methyl silsesquioxane. 